The present invention is directed to brushless electric motors. More specifically, the present invention is directed to device and method for reducing stray AC magnetic fields generated by linear brushless electric motors. The linear brushless electric motors are particularly useful for moving stages in charged particle lithography, inspection and/or measurement tools.
Linear motors are used in a variety of electrical devices. For example, photolithography systems and other semiconductor processing equipment utilize linear motors to precisely position a reticle stage holding a reticle and a wafer stage holding a wafer. Alternately, linear motors are used in other devices, including elevators, machine tools, metal cutting machines, and inspection machines.
A typical brushless electric motor includes a magnet component and a conductor component. The magnet component includes a plurality of permanent magnets positioned side-by-side each of which generates a surrounding magnetic field. The conductor component includes a plurality of motor drive coils. When electric current flows in the motor drive coils, a Lorentz type force is created in a direction mutually perpendicular to the direction of the motor drive coils and the magnetic field of the magnets. The force can be used to move one of the components relative to the other component of the motor.
During operation, a typical brushless linear electric motor generates stray magnetic fields external to the motor. Unfortunately, a number of manufacturing, measurement and/or inspection processes are influenced by stray AC or more generally time dependant magnetic fields. For example, electron beams are influenced by AC magnetic fields of sufficient magnitude. Thus, with current motor designs, AC brushless linear electric motors must be positioned a relatively large distance away from an electron beam, typically outside a system magnetic shield.
Recently, requirements of higher performance require the electric motors be integrated directly into the stages. This means the motors must be positioned within the magnetic shield and close to the electron beam. As a result thereof, the stray AC magnetic fields from the motors present a problem.
One attempt to solve this problem includes adding one or more additional magnetic shields that block the stray AC magnetic fields from the motor. Unfortunately, the magnetic shields will require a sizable opening to allow for movement of the moving part of the motor. Further, the magnetic shields can increase the size of the motor. This increases the size and weight of the entire tool.
In light of the above, it is an object of the present invention to provide a brushless electric motor that has reduced stray magnetic fields. Another object is to provide a brushless electric motor for an exposure apparatus that utilizes a charged particle beam. Yet another object is to provide an improved motor for precisely positioning a device during a manufacturing, measurement and/or an inspection process. Still another object of the present invention is to provide a method for decreasing stray magnetic fields without significantly influencing the dynamic performance of the motor and without significantly increasing the size of the motor. Yet another object of the present invention is to provide a conductor component for an electric motor that reduces the stray magnetic fields of the motor. Another object is to provide an exposure apparatus capable of manufacturing precision devices, such as high density, semiconductor wafers.
The present invention is directed to an electric motor and a conductor component that satisfies these objects. The electric motor includes a magnet component and a control system in addition to the conductor component The magnet component includes one or more magnets that generate surrounding magnetic fields. The conductor component includes a motor drive conductor array that interacts with the magnet component to move one of the components relative to the other component of the electric motor. More specifically, the control system directs electric current to the motor drive conductor array. When electric current flows in the motor drive conductor array, a reaction force is generated that is used to move one of the components relative to the other component of the electric motor.
Uniquely, the conductor component also includes an auxiliary conductor array. As provided herein, when current is directed through the auxiliary conductor array, the auxiliary conductor array generates an auxiliary electro-magnetic field that interacts with a stray magnetic field of the motor and reduces the stray magnetic field of the motor. As a result of this design, the magnitude of the stray magnetic field of the brushless electric motor is reduced. Thus, the motor provided herein is particularly useful in manufacturing, measurement and/or inspection processes that are sensitive to and/or influenced by stray AC magnetic fields.
In a preferred embodiment, the auxiliary conductor array includes one or more auxiliary coils that are (i) positioned near the motor drive conductor array, (ii) positioned to have substantially no effect on the performance of the motor, and (iii) designed to not significantly influence the size and thickness of the conductor component.
In one embodiment, the auxiliary conductor array substantially encircles the motor drive conductor array. In this embodiment, the auxiliary conductor array includes a left transverse segment and a right transverse segment that is spaced apart from the left transverse segment along the direction of motor travel. Importantly, the transverse segments are positioned so when current is directed through the auxiliary conductor array, the left transverse segment, generates a force that is substantially equal and opposite to a force generated by the right transverse segment. With this design, the auxiliary conductor array does not significantly influence the performance of the motor.
Alternately, in another embodiment, the auxiliary conductor array includes four spaced apart coil sets that cooperate to substantially encircle the motor drive conductor array in its plane. This design is particularly useful when the motor drive conductor array includes an even number of motor drive coils.
Additionally, in the designs provided herein, the conductor component includes a conductor component housing that retains the motor drive conductor array and the auxiliary conductor array.
In the designs provided herein, the magnet component includes a pair of spaced apart magnet arrays and the motor drive conductor array is positioned between the magnet arrays. Further, the auxiliary conductor array is positioned between the magnet arrays.
The present invention is also directed to a method for manufacturing a brushless electric motor, a stage assembly, an exposure apparatus and a method for making a device utilizing the exposure apparatus.